title: Functional role of the MrpA- and MrpD-homologous protein subunits in enzyme complexes evolutionary related to respiratory chain complex I.
abstract: NADH:quinone oxidoreductase or complex I is a large membrane bound enzyme complex that has evolved from the combination of smaller functional building blocks. Intermediate size enzyme complexes exist in nature that comprise some, but not all of the protein subunits in full size 14-subunit complex I. The membrane spanning complex I subunits NuoL, NuoM and NuoN are homologous to each other and to two proteins from one particular class of Na(+)/H(+) antiporters, denoted MrpA and MrpD. In complex I, these ion transporter protein subunits are prime candidates for harboring important parts of the proton pumping machinery. Using a model system, consisting of Bacillus subtilis MrpA and MrpD deletion strains and a low copy expression plasmid, it was recently demonstrated that NuoN can rescue the strain deleted for MrpD but not that deleted for MrpA, whereas the opposite tendency was seen for NuoL. This demonstrated that the MrpA-type and MrpD-type proteins have unique functional specializations. In this work, the corresponding antiporter-like protein subunits from the smaller enzymes evolutionarily related to complex I were tested in the same model system. The subunits from 11-subunit complex I from Bacillus cereus behaved essentially as those from full size complex I, corroborating that this enzyme should be regarded as a bona fide complex I. The hydrogenase-3 and hydrogenase-4 antiporter-like proteins on the other hand, could substitute equally well for MrpA or MrpD at pH7.4, suggesting that these enzymes have intermediate forms of the antiporter-like proteins, which seemingly lack the functional specificity.
authors.affiliation: Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, PO Box 124, S-221 00 Lund, Sweden.
authors.forename: Vamsi K
authors.initials: VK
authors.lastname: Moparthi
authors.forename: Brijesh
authors.initials: B
authors.lastname: Kumar
authors.forename: Yusra
authors.initials: Y
authors.lastname: Al-Eryani
authors.forename: Eva
authors.initials: E
authors.lastname: Sperling
authors.forename: Kamil
authors.initials: K
authors.lastname: Górecki
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Drakenberg
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hägerhäll
mesh_terms: D001407:Bacillus / Q000737:chemistry; D004579:Electron Transport; D042967:Electron Transport Complex I / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000201:enzymology; D006864:Hydrogenase / Q000737:chemistry; D008566:Membranes / Q000737:chemistry / Q000201:enzymology; D009097:Multienzyme Complexes / Q000737:chemistry*; D021122:Protein Subunits / Q000737:chemistry; D017494:Proton Pumps / Q000737:chemistry; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; D021122:Protein Subunits; D017494:Proton Pumps; D017923:Sodium-Hydrogen Exchangers; D006864:Hydrogenase; D042967:Electron Transport Complex I
keywords: 11-subunit complex I; Membrane-bound hydrogenase; Mrp-complex; NADH:quinone oxidoreductase; Na+/H+ antiporter